The present invention is in the area of methods for fabricating molds to be used in manufacturing molded medical products, wherein the molds are fabricated using computer-aided design (CAD) in combination with solid free-form fabrication (SFF) technology. More particularly, the present invention is in the area of methods for fabricating molds for making molded tissue products.
Solid free-form fabrication (SFF) techniques are known which can be used to manufacture complex objects from a variety of materials. These objects can be used as articles of manufacture themselves, or they can be used as molds to create molded articles. The SFF methods can be adapted for use with a variety of polymeric, inorganic and composite materials to create mold structures with defined compositions, strengths, and densities, using computer aided design (CAD).
SFF techniques include stereo-lithography (SLA), selective laser sintering (SLS), ballistic particle manufacturing (BPM), fusion deposition modeling (FDM), and three dimensional printing (3DP). The present invention can be practiced with any of these SFF techniques. A preferred way of practicing the invention is with the use of three dimensional printing for fabricating the molds of the invention. 3DP is used to create molds which can be used for molding products which comprise tissue from human or other animal sources. SFF techniques can be used to form molds which have at lease one porous portion on the interior surface of the molds, where these porous portions are in communication with the exterior of the molds. According to the teachings of the invention, tissue materials can be molded into a broad variety of shapes by introducing a mixture containing tissue material into the interior of a mold according to the teachings of the invention with the tissue material mixed with one or more fluid tissue matrix components. The fluid tissue matrix component or components can be withdrawn from the tissue material through the porous portion of the mold, to the exterior of the mold. A molded tissue product is thereby produced which can be then released from the mold. Optionally, one or more additives may be included in the pore space of the mold of the invention before carrying out molding of a tissue product, and the additive if used can be removed during the molding process by withdrawing the additive through the porous structure of the mold to the mold exterior.
The macrostructure and porosity of the mold can be manipulated by controlling printing parameters, the type of polymer and particle size, as well as the solvent and/or binder. Porosity of the matrix walls, as well as the matrix per se, can be manipulated using SFF methods, especially 3DP.
SFF methods can be used to fabricate a mold which can then be used for the subsequent fabrication of a tissue product to be used in patients. The tissue product to be made can be composed primarily of tissue, can be composed primarily of substitute tissue products, or can be composed of a blend or mixture of natural and synthetic materials intended to replace tissue in a patient. The fabrication of this tissue product using such a mold may be done using either gravity or pressure casting or molding techniques. According to the teachings of the present invention, at least one portion of the interior surface of the SFF prepared mold is porous and in porous communication with the exterior of the mold of the invention. The mold of the invention allows casting or molding of a tissue product to be more easily carried out because a more fluid mixture of tissue containing material can be introduced into a mold of the invention. Excess fluid or other excess components of the mixture containing the tissue material can be drawn from the mold selectively through the porous interior surface portion of the mold, concentrating the tissue product within the interior of the mold. Means for removing the excess fluid or other components can include a simple pump, such as a piston or rotary pump. A rough analogy to the method of the invention may be made to slip casting in the ceramics industry, where a ceramic material with excess water (slip) is introduced into a mold for pourability and then the excess water is extracted through the walls of the ceramic mold. By applying SFF processes to the fabrication of a mold, the mold itself can incorporate features which allow selected components of a tissue mixture to be molded to be absorbed or extracted through the walls of the mold. This permits a tissue mixture to comprise a component to facilitate pouring or injecting of the tissue mixture into the mold, with the ability to reduce or extract a selected component from the tissue mixture once the mixture is in the mold, enabling improved or augmented implantation or operating characteristics of the final molded tissue product.
Using the teaching of the present invention, a SFF fabricated mold is used to fully or selectively control the materials composition of the mold itself as well as the micro- and macro-architecture of the mold. For example, the mold may be fabricated from a ceramic material which is made with a microstructure that will selectively allow the absorption or extraction of fluid from a tissue mixture, such fluid having been mixed with the tissue to facilitate pouring or injection of the mixture into the mold. The porosity of the mold can be varied depending on the tissue mixture component to be extracted, or channels or pores may be introduced in certain areas of the mold as the mold is being fabricated, to allow extraction of tissue mixture components only from selected regions of the tissue being molded. A main advantage of the present invention is that it allows a tissue containing mixture to be formulated for flowability into a mold, along with the ability to absorb or extract selected components from said mixture during the molding process, optimizing the actual final tissue product""s characteristics. This is a significant advance from conventional approaches for molding tissue products, which are currently molded using non-porous molds. The conventional method for molding tissue products requires that the tissue/additive composition ratio remain the same throughout the molding or casting process and in the final molded or cast product. This results in a compromise being made between the ease of molding and the desired properties of the final tissue product. And, since SFF techniques such as three dimensional printing are used to fabricate a mold, product geometries that are unavailable using conventional mold approaches or machining methods can be readily achieved. Such geometries include undercuts, overhangs and recurved surfaces.